JPS6028601A - Prism type beam splitter - Google Patents

Abstract

PURPOSE:To enhance performance with a simple structure by forming a light semitransmitting film composed of four layers of the first dielectric layer, the second dielectric layer, a silver metal layer, and the third dielectric layer between prisms. CONSTITUTION:A light semitransmitting film HM is formed between the junction layers of two right triangular prisms 2, 4 of n0 refractive index. This film HM is composed of the four layers of the first dielectric layer having a refractive index of n1, and an optical film L1, the second dielectric layer L2 having n2 and n2d2, a silver metal layer, and the third dielectric layer having n3 and n3d3, thickness of n1d1. C in the figure is an adhesive layer. The following relationships are satisfied: n0<n1<=n3, n0<n2<=n3, 0.3<¦n1-n2¦<0.7, 0.05lambda0<n1d1=n2d2<0.10lambda0, n3d3 =0.25lambda0, where lambda0 is the designed wavelength of light selected within the range of 400-700nm. The algebraic film thickness of the silver metal layer is selected within the range of 10-50nm in accordance with a desired ratio of reflectance to transmittance.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a prismatic beam spotting device used in single-lens reflex cameras, cine cameras, etc. in which exposure control and focus detection are performed by TTL photometry.

Conventional technology Previously, as a prism type beam suburi-tsuta,
6-27106 Publication m1 diagram implementationllAl lAs described, the first prism is made of glass with a refractive index of 1.52 and the second prism is made of glass with a refractive index of 1.56. From the prism side to the @2 prism side, a light semi-transparent film consisting of five layers: a refractive index dielectric layer, a medium refractive index dielectric layer, an Ag layer, a medium refractive index dielectric layer, and a high refractive index dielectric layer is formed. A prismatic beam splitter having a five-layer structure is known.

Although this conventional device has excellent optical performance in that the spectral characteristics are flat in the visible wavelength range and is less affected by polarization, it has the disadvantage that it has a large number of layers and is not easy to manufacture.

Purpose The present invention has been made to improve the drawbacks such as "double layer", and its purpose is to obtain almost the same optical performance as the above-mentioned conventional device with a four-layer structure.

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a first glass plate made of glasses having substantially the same refractive index. In a prismatic beam splitter in which a light semi-transparent film is formed between the second prism, the light semi-transmissive film is formed in order from the first prism side to the second prism side: a first dielectric layer made of a dielectric; A second dielectric layer.

It has a four-layer structure including a metal layer 2 made of Ag and a third dielectric layer made of a dielectric, and the refractive index of the first prism is no.
, the refractive indexes of the first to third dielectric layers are old, old, old, and the optical thicknesses are old d+, nzd3n3d3, and 4.
When the design wavelength selected within the range of 00 to 700 plates is λO, it is characterized by satisfying the following conditions.

no<n+≦03 no(n2≦03 0.3<Int-nzI<Q, 70.05λo
< n+dt = n2d2< Q, 10λ0n3d
3=Q, 25λO Examples Examples of the present invention will be described in detail below.

FIG. 1 is a diagram showing a prism type beam splitter according to an embodiment of the present invention. In the same figure, (2) and (41) are right triangular semi-transparent films (H) made of the same glass and having the same shape.
M) is connected from the first prism (21 side) to the second prism (41 side).
In this order, a first dielectric layer (Ll) made of a dielectric, a second dielectric layer (Ll) made of a dielectric, a metal layer (Ag) made of Ag, and a third dielectric layer made of a high refractive index dielectric. Body layer (
La) has a four-layer structure. The first to third dielectric layers (Ll) (Ll) (La) are all connected to the first prism (2).
), and the third dielectric layer (La) has the same or higher refractive index than the first and second dielectric layers (Ll) (Ll). The refractive index difference between the first dielectric layer (Ll) and the second dielectric layer (Ll) is 0.3 to 0.7.

The optical thickness of the I81 dielectric layer (Ll) is the same as that of the second dielectric layer (Ll).
Ll) and 0.05λ0~0. Very thin, lOλ0. The optical thickness of the third dielectric layer (La) is 0.25λ
〇-C1 metal layer (Ag) has a geometric thickness of 10 to 50n
It is determined within the range of m depending on the desired reflectance:transmittance ratio. (C1 is an adhesive layer. Note that an adhesive layer + CI may be provided between the C41 prism (2) and the first dielectric layer (Ll).

- The beam substratum shown in FIG. It is manufactured by sequentially forming the prisms by vacuum evaporation and then bonding them to the second prism (4) with an adhesive.

In the beam splitter as described above, the first prism (
2) Light incident from the side (the moon is split into two by a semi-transparent film (HM) into reflected light [R1 and transmitted light +T+].

Incidentally, even if light is incident from the second prism (4) side, almost the same optical characteristics can be obtained.

Specific configurations of various embodiments of the present invention are shown in tables below.

Example 1゜λo = 55Qnm Fig. 2 shows the spectral characteristics when light with an incident angle of 45° is incident from the first prism (2) side of this example.

In Figure 2, R3 is the reflectance of the S-wave component, Rp is the reflectance of the P-wave component, TS is the transmittance r of the S-wave component, and T9 is the P
The transmittance of each wave component is shown. As is clear from FIG. 2, according to this example, both the reflectance and the transmittance change smoothly within 10% over the entire visible wavelength range, and the spectral characteristics are flat. TS and Tp
Since the difference between angle of incidence 4
The spectral characteristics when light is incident at an angle of 5° are shown in FIG. 3 in the same manner as in FIG. As shown in Figure 3,
In this example, both the change in reflectance and the change in transmittance in the entire visible wavelength range are gentle within 10%, and a flat spectral characteristic power 5 is obtained, and the differences between Rs and Rp and between Ts and Tp are also Since there are only four elements, there is little influence of polarization, and there is also little optical loss due to absorption, making it possible to obtain the same prior performance as the conventional device with a smaller number. In particular, in this example, the overall reflectance is increased and the transmittance is decreased compared to the implementation f11 having the performance shown in FIG.
Moreover, the difference in polarization components is small on the long wavelength side, and G'1 characteristics can be obtained.

(Left below) Example 3 In this example, AlzO3 and Zro2 in Example 2 were replaced, and the adhesive layer FC+ was replaced by $1 prism +
21 & the first dielectric layer (Ll).

Figure $4 shows the spectral characteristics when light with an incident angle of 45° is incident from the first prism (2) side of this example. As is clear from FIG. 4, in this example, both the change in reflectance and the change in transmittance in the entire visible wavelength range were only about 10%, and flat spectral characteristics were obtained, and R3 and Rp Also, the difference between Ts and Tp is about 5% each, so there is little influence of polarization, and there is little optical loss due to absorption L)
. Therefore, it is possible to obtain almost the same optical performance as the conventional device described above. In particular, in this embodiment, it is possible to set both the reflectance and the transmittance to around 50%.

Incidentally, as in Examples 1 to 3 above, the first dielectric layer (LI)
Or the second dielectric layer (Ll) and the third dielectric main layer (L3
) are made of the same material, even though it has a 1-4 layer structure, only 3 types of evaporation materials C are required during manufacturing.
Manufacturing can be simplified.

Note that TiOz, CeO2, ZnS, etc. may be used instead of ZrO2.

FIG. 5 shows a prismatic beam diffuser according to the present invention.

In this example, the light transmitted through the photographic lens (TL) is split into two by the beam splitter (BS), the transmitted light is guided to the film surface (Fl), and the reflected light is Finder system (FS) + conductivity).

Effects As described above, according to the present invention, both reflectance and transmittance have flat spectral characteristics over the entire visible wavelength range, and the optical system is almost equivalent to the conventional device with a five-layer structure, which is less affected by polarization. Performance can be obtained with a four-layer configuration, making manufacturing easier.

Historically, when the first dielectric layer or the second dielectric layer and the third dielectric layer are made of the same material as in the embodiment, 4
Despite the layered structure, only three types of vapor deposition materials are required;
Easy to manufacture.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a prism type beam splitter according to an embodiment of the present invention, and FIGS. 2 to 4 are respectively embodiment 1.
FIG. 5 is a diagram showing the spectral characteristics of light at an incident angle of 45° in the range of 1 to 3, and FIG. (21, 1st prism, +41 i 2nd prism, (
HM); light semi-transparent film, (Ll); first dielectric layer,
(L2); Second dielectric layer, (Ag); Metal layer, (L
3); Third dielectric layer. Ganto Kamiyama Minolta Camera Co., Ltd.

Claims (1)

[Claims] In a prism type beam splitter in which a light semi-transparent film is formed between first and second prisms made of glass having substantially the same refractive index, the light semi-transparent film is formed from the first prism side. The second prism side has a 4-layer structure consisting of a 951 dielectric layer made of a dielectric, a second dielectric layer made of a dielectric, a metal layer made of Ag, and a third dielectric layer made of a dielectric, in order:
And, a prism type beam splitter characterized by adding 71.1111 of the following conditions: □□□□□□□□□ +1o(n+≦03 +10(n2≦113 0.3<ln+ -1121<0. 70.05λ
o (n+d+ = n2d2< 0.10λOr+a
d3=0.25λ0 However, here: no H first prism refractive index. Old: refractive index of the first dielectric layer. n2: refractive index of the second dielectric layer. n3; @3 refractive index of dielectric layer. n+dt; optical thickness of the first dielectric layer. nzd2; optical thickness of the second dielectric layer. n3da; optical thickness of the third dielectric layer. λO; Design wavelength selected within the range of 4QQnm to 700 nm. It is.